Enzyme-linked immunosorbent assay to differentiate the antibody responses of animals infected with Brucella species from those of animals infected with Yersinia enterocolitica O9

Evaluation of chimeric proteins for serological diagnosis of brucellosis in cattle

Background and Aim

An accurate diagnosis of Brucella-infected animals is one of the critical measures in eradication programs. Conventional serological tests based on whole-cell (WC) antigens and detecting antibodies against pathogen-associated lipopolysaccharide might give false-positive results due to the cross-reactivity with other closely related bacteria. This study evaluated the serological potential of Brucella spp. chimeric outer membrane proteins (Omps) as antigens in an indirect enzyme-linked immunosorbent assay (i-ELISA).

Materials and Methods

The chimeric gene constructs of the most immunodominant regions of Brucella Omps 25+31, 25+19, and 19+31 were cloned into the pET28a expression vectors and transformed into Escherichia coli BL21 (DE3). The serological potential of chimeric proteins compared with single recombinant Omps (rOmps)19, 25, and/or 31 were studied on blood serum samples of (i) a rabbit immunized with killed Brucella abortus 19WC, (ii) mice immunized with single rOmps, (iii) cows seropositive for brucellosis by rose Bengal test, and (iv) cattle naturally and/or experimentally infected with brucellosis.

Results

E. coli BL21 actively produced Brucella chimeric rOmps, the concentration of which reached a maximum level at 6 h after isopropyl-b-D-1-thiogalactopyranoside stimulation. Target proteins were antigenic and expressed in an active state, as recognized by rabbit anti-B. abortus antibodies in an i-ELISA and western blotting. Murine antibodies against the single rOmps reacted with chimeric antigens, and conversely, antichimeric antibodies found their epitopes in single proteins. Brucella chimeric rOmps showed higher antigenicity in blood sera of seropositive cattle kept in the hotbed of the infection and/or experimentally challenged with brucellosis than single proteins.

Conclusion

Brucella chimeric recombinant outer membrane proteins could be a potential antigen candidate for developing an ELISA test for accurate diagnosis of bovine brucellosis.

Soliman H, I. Mohamed H, A. Salem M, A. Ahmed S. Diagnostic performance of RFLP-PCR and sarcosine based indirect ELISA versus immunoassays in Brucella infected and vaccinated small ruminants

This study was carried out for evaluation of the diagnostic performance of different serological assays; buffered acidified plate antigen test (BAPAT), rose bengal plate test (RBPT), immunochromatographic assay (ICA), rivanol test (RivT), indirect ELISA using two types of coating antigens (smooth lipopolysaccharide; S-LPS and N-lauroylsarcosine-extracted antigens; SE) and complement fixation test (CFT). Relative sensitivity and specificity of various techniques were estimated. The traditional serological tests failed to distinguish the vaccinated from naturally infected animals. Using iELISA with extracted antigens (SE) as a coating antigen was a more accurate test to differentiate the naturally infected animals from vaccinated animals. Application of restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) on sera samples from seropositive animals, Rev-1 vaccinated sheep and Brucella field strain infected sheep and goats revealed that there were samples identified as B. melitensis biovar 3 field strain and other samples identified as B. melitensis Rev-1 vaccinal strain. The obtained results established that restriction fragment length polymorphism-polymerase chain reaction can differentiate between animals infected with Brucella field strains from animals vaccinated with the Rev-1 vaccine.

Epidemiological and clinical characteristics of neurobrucellosis case patients in Tunisia

OBJECTIVE

We aimed to identify epidemiological, clinical, therapeutic, diagnostic, and outcome characteristics of neurobrucellosis case patients in Tunisia.

PATIENTS AND METHODS

We conducted a retrospective and descriptive study over a 17-year period (January 1997-December 2013). We included all neurobrucellosis patients hospitalized in the infectious disease department of La Rabta Hospital of Tunis during the study period.

RESULTS

A total of 13 patients were included in the study: 9 men and 4 women. Mean age was 31.6 years. Six patients presented with meningitis, three with encephalitis, two with meningoencephalitis, and two with meningo-myeloradiculitis. All patients had a lumbar puncture performed. Eleven patients had an abnormal cerebrospinal fluid (CSF) (84.6%): lymphocytic pleocytosis in seven patients, high level of CSF proteins in 11, and low level of CSF glucose in seven. All patients had a positive Brucella serological test in blood. A Brucella serological test was also performed in CSF and was positive for 10 patients (77%). A total of nine patients had a cerebral CT scan and/or MRI performed and abnormalities were observed in six patients. Antibiotic therapy was prescribed to all patients: a combination of rifampicin and co-trimoxazole (n=9) or doxycycline (n=4) for an average duration of eight months. Two patients also received steroids. A positive outcome was observed in 10 patients. Three patients were lost to follow up.

CONCLUSION

Brucellosis may be severe when neurological involvement occurs. Brucellosis should be considered in the event of any neurological involvement associated with suggestive epidemiological features.

Microplate Agglutination Test for Canine Brucellosis Using Recombinant Antigen-Coated Beads

Brucella canis, a facultative intracellular pathogen, is the causative agent of canine brucellosis. The diagnosis of canine brucellosis is based on bacteriological examination and serological methods, including agglutination and gel diffusion tests. In this study, four recombinant antigens, heat shock protein 60, rhizopine-binding protein, Cu-Zn superoxide dismutase, and hypothetical protein (Ag 4), were constructed. These antigens were coated on latex beads and their usefulness in the serological diagnosis of canine brucellosis was examined. All recombinant antigens showed specific reaction with sera from B. canis-infected dogs in Western blotting. In a microplate agglutination test, mixing sera from B. canis-infected dogs, but not sera from B. canis-free dogs, with single or multiple antigens-coated latex beads produced clear agglutination. Moreover, the antigen-coated latex beads did not show nonspecific agglutination in hemolyzed serum samples. A survey of canine serum samples conducted by the microplate agglutination test using single antigen-coated latex beads showed that this method would be useful in the serological diagnosis of canine brucellosis. Further investigations using more serum samples are required to confirm the usefulness of our method.

Protective effects of recombinant Brucella abortus Omp28 against infection with a virulent strain of Brucella abortus 544 in mice

The outer membrane proteins (OMPs) of Brucella (B.) abortus have been extensively studied, but their immunogenicity and protective ability against B. abortus infection are still unclear. In the present study, B. abortus Omp28, a group 3 antigen, was amplified by PCR and cloned into a maltose fusion protein expression system. Recombinant Omp28 (rOmp28) was expressed in Escherichia coli and was then purified. Immunogenicity of rOmp28 was confirmed by Western blot analysis with Brucella-positive mouse serum. Furthermore, humoral- or cell-mediated immune responses measured by the production of IgG1 or IgG2a in rOmp28-immunized mice and the ability of rOmp28 immunization to protect against B. abortus infection were evaluated in a mouse model. In the immunogenicity analysis, the mean titers of IgG1 and IgG2a produced by rOmp28-immunized mice were 20-fold higher than those of PBS-treated mice throughout the entire experimental period. Furthermore, spleen proliferation and bacterial burden in the spleen of rOmp28-immunized mice were approximately 1.5-fold lower than those of PBS-treated mice when challenged with virulent B. abortus. These findings suggest that rOmp28 from B. abortus is a good candidate for manufacturing an effective subunit vaccine against B. abortus infection in animals.

Interference in diagnostic tests for brucellosis in cattle recently vaccinated against leptospirosis

The aim of the current study was to verify if cattle vaccinated against leptospirosis may react in diagnostic tests for brucellosis. Sixty cows were divided into 5 groups, each comprising 12 animals. Four groups were given different vaccines against leptospirosis, while the control group received only saline. Two doses of vaccine were given, as recommended by the manufacturers. Serum samples were collected on the first day of immunization (day 0) and on postvaccination days 7, 14, 21, 28, 35, 42, 49, 56, 96, and 126. All the serum samples were tested for brucellosis and leptospirosis. Twenty animals were reactive at least once to the Rose Bengal test, but by day 96, no further reactions were elicited by this test. Twenty-six samples were reactive to the Rose Bengal test, but only 7 remained positive in confirmatory tests: 1 to the 2-mercaptoethanol test, 2 to the fluorescence polarization assay, and 6 to indirect enzyme-linked immunosorbent assays. None of the samples was reactive in the complement fixation test. None of the animals in the control group was reactive. A significant difference was found between the control group and the groups vaccinated against leptospirosis, according to Fisher exact test. However, the groups were found to respond independently of the vaccine brand. The results indicate that cattle vaccinated against leptospirosis may show reactivity on screening tests for brucellosis.

Herd prevalence of bovine brucellosis and analysis of risk factors in cattle in urban and peri-urban areas of the Kampala economic zone, Uganda

Background

Human brucellosis has been found to be prevalent in the urban areas of Kampala, the capital city of Uganda. A cross-sectional study was designed to generate precise information on the prevalence of brucellosis in cattle and risk factors for the disease in its urban and peri-urban dairy farming systems.

Results

The adjusted herd prevalence of brucellosis was 6.5% (11/177, 95% CI: 3.6%-10.0%) and the adjusted individual animal prevalence was 5.0% (21/423, 95% CI: 2.7% - 9.3%) based on diagnosis using commercial kits of the competitive enzyme-linked immunosorbent assay (CELISA) for Brucella abortus antibodies. Mean within-herd prevalence was found to be 25.9% (95% CI: 9.7% - 53.1%) and brucellosis prevalence in an infected herd ranged from 9.1% to 50%. A risk factor could not be identified at the animal level but two risk factors were identified at the herd level: large herd size and history of abortion. The mean number of milking cows in a free-grazing herd (5.0) was significantly larger than a herd with a movement restricted (1.7, p < 0.001).

Conclusions

Vaccination should be targeted at commercial large-scale farms with free-grazing farming to control brucellosis in cattle in and around Kampala city.

Enzyme-linked immunosorbent assay for screening of canine brucellosis using recombinant Cu-Zn superoxide dismutase

Brucella canis, a facultative intracellular pathogen, is the causative agent of canine brucellosis. The diagnosis of canine brucellosis is based on bacteriological examination and serological methods including agglutination and gel diffusion tests. In this study, recombinant B. canis Cu-Zn superoxide dismutase (SOD) was used as an antigen for the enzyme-linked immunosorbent assay (ELISA). The recombinant SOD showed a specific reaction with serum infected with B. canis in Western blotting and ELISA. These results suggest that ELISA using recombinant SOD is useful in screening for canine brucellosis.

Cold-induced gene expression profiles of Vibrio parahaemolyticus: a time-course analysis

A whole-genome DNA microarray was constructed to dissect expression profiles of Vibrio parahaemolyticus in response to a sudden temperature downshift from 37 to 10 degrees C. The mRNA level of each gene at each of three time points (20, 40 and 60 min after temperature downshift) was compared with that just before cold treatment. Clustering analysis of time-course data revealed nine gene clusters with different time-dependent expression patterns. Downregulation of metabolism-related genes was obviously dominant over upregulation at all time points. The distinct negative regulation of metabolism-related genes would account for a generally reduced cellular protein pool resulting from the sudden temperature downshift. In contrast, cold shock had a 'neutral and balanced' regulatory action on nonmetabolic cellular pathways, which likely brought about the remodelling of cell envelope structures and transport/binding functions. We identified a 171-bp 5'-untranslated region in the cspA transcript. The cspA gene encoded cold shock protein A (CspA), and CspA was shown to be the major cold shock protein in V. parahaemolyticus. Evident regulatory motifs were conserved within the cspA promoter regions of Escherichia coli and V. parahaemolyticus. These two bacteria likely use the same mechanism to regulate the cold-inducible expression of cspA.

Investigation for presence of Neospora caninum, Toxoplasma gondii and Brucella-species infection in killer whales (Orcinus orca) mass-stranded on the coast of Shiretoko, Hokkaido, Japan

Twelve killer whale (Orcinus orca) were hemmed in by ice floes, and nine died on the Aidomari coast in the Nemuro Strait in Rausu, Shiretoko, Hokkaido, Japan on 8 February 2005. Tissue samples collected from 8 whales were tested for Neospora caninum, Toxoplasma gondii, and Brucella species DNA by polymerase chain reaction (PCR) assay. Gamma-globulin isolated from blood samples by ammonium sulfate precipitation was tested for antibodies to these pathogens by means of agglutination tests and immunoblotting. None of the 8 tissue samples had antibodies to the pathogens, when subjected to agglutination tests. In immunoblotting, one sample (sample No.5) showed antibody binding to N. caninum antigens. In the PCR assay, none of the samples was positive. Further study is necessary to examine the prevalence of the pathogens in marine mammals inhabiting this area.

A Rapid Agglutination Assay for Canine Brucellosis Using Antigen Coated Beads

Brucella canis is the causative agent of canine brucellosis and facultative intracellular pathogen. The diagnosis of canine brucellosis is based on bacteriological examination and serological methods including agglutination and gel diffusion tests. In this study, crude antigens were extracted from B. canis using hot saline, coated on to latex beads and their usefulness in the serological diagnosis of canine brucellosis was examined. Mixing the antigen coated latex beads with the sera of dogs infected with B. canis produced clear agglutination, but this was not so for B. canis free dog sera. N-terminal amino acid sequence analysis of the crude hot saline extracts, showed that they contained copper-zinc superoxide dismutase, ribose ABC transporter and hypothetical protein of Brucella as antigens. A serological survey of canine serum samples conducted by means of an agglutination test using the antigen coated latex beads, showed that this method was more specific than the tube agglutination test using whole bacterial cell antigens. Although these results suggest that our method in which crude hot saline extracted antigens are coated on to latex beads would be useful in the serological diagnosis of canine brucellosis, we need further investigation using more serum samples to confirm the usefulness of our method.

A serological survey of Brucella spp. in free-ranging wild boar (Sus scrofa leucomystax) in Shikoku, Japan

Brucella, a causative agent of brucellosis and facultative intracellular pathogen, has been isolated recently from a variety of wild mammals. In this study, serum samples from 115 Japanese wild boar (Sus Scrofa leucomystax) killed by hunters in the 4 Prefectures of Shikoku, Japan were tested for antibodies to Brucella spp. by means of the tube agglutination test (TAT) and enzyme-linked immunosorbent assay (ELISA) using antigens extracted with n-lauroylsarcosine. In 9 of the 115 samples (7.8%) antibodies to Brucella spp. were detected by TAT and ELISA. These results suggest that wild boar in Shikoku may be exposed to Brucella spp. or other cross-reactive pathogen infection.

Development and Validation of a Competitive ELISA Kit for the Serological Diagnosis of Ovine, Caprine and Bovine Brucellosis

A competitive ELISA (Brucella-Ab c-ELISA) was standardized and validated for the detection of Brucella antibodies in cattle, sheep and goat sera using a monoclonal antibody (MAb 4B5A) produced against Brucella melitensis biotype 2. The specificity and sensitivity of the assay were 100% to a 67.5% cut-off point (B/Bo%). When compared with an indirect ELISA, the Brucella-Ab c-ELISA did not demonstrate cross-reactions when testing positive sera for antibodies to some Enterobacteriaceae. A comparison was made between the Brucella-Ab c-ELISA and the complement fixation and Rose Bengal tests. Results demonstrated that the Brucella-Ab c-ELISA is a valuable tool for the serological diagnosis of bovine and ovine/caprine brucellosis.

Evaluation of a western blot method for the detection of Yersinia antibodies: evidence of serological cross-reactivity between Yersinia outer membrane proteins and Borrelia burgdorferi

Yersinia enterocolitica and Yersinia pseudotuberculosis have been identified as causative organisms of reactive arthritis in humans. We evaluated a Western blot assay which uses Yersinia outer membrane proteins as antigens for the detection of Yersinia antibodies as a replacement for the complement fixation (CF) assay. Clinical agreement, sensitivity, and specificity were determined by testing 19 positive and 21 negative serum samples by the CF assay, Western blot assay, and enzyme-linked immunosorbent assay (ELISA). The CF assay and ELISA were compared to the Western blot assay, which was the reference method used in this study. Sera with antibodies that could potentially cross-react with Yersinia were also tested by the Western blot assay. The agreement, sensitivity, and specificity of the CF method were 61%, 26%, and 95%, respectively; and those for the ELISA were 89%, 95%, and 82%, respectively. The prevalences of Yersinia antibodies in 50 healthy donors were 6% for immunoglobulin G (IgG), 2% for IgA, and 2% for IgM. Sera positive for Bartonella henselae, Brucella, Chlamydia pneumoniae, and Rickettsia rickettsii antibodies showed cross-reactivity by the Western blot assay. The highest cross-reactivity was observed with Borrelia burgdorferi; 5 of 11 (45%) specimens were cross-reactive by the IgM-specific assay. Overall, the Western blot assay performs acceptably and is more sensitive than the CF assay, warranting replacement of the CF assay in the laboratory. Due to the evidence of cross-reactivity, particularly with B. burgdorferi, which can cause an oligoarthritis similar to reactive arthritis, the diagnosis of reactive arthritis should be based on clinical findings and complete serologic analysis of the potential causative infectious pathogens.

Differentiation between serological responses to Brucella suis and Yersinia enterocolitica serotype O:9 after natural or experimental infection in pigs

False-positive serological reactions (FPSR) due to infections with Yersinia enterocolitica serotype Oratio9 (YeOratio9) are a problem in tests for brucellosis. In the present study, FPSR in classical and novel tests for brucellosis following experimental infections of pigs with YeOratio9 were compared with responses of B. suis biovar 2-inoculated pigs. FPSR were limited to 2-9 weeks post-YeOratio9 inoculation, while B. suis-infected pigs were test-positive throughout the 21-week period of investigation. Although YeOratio9-inoculated pigs exhibited FPSR in Brucella tests for a limited period of time, the serological responses in a YeOratio9-purified O-antigen indirect ELISA did not decrease accordingly. Analysis of available cross-sectional serum samples from pig herds naturally infected with YeOratio9 or B. suis biovar 2 confirmed that the observed difference in the duration of the serological responses between the two infections could be used to discriminate between herds infected with B. suis biovar 2 and YeOratio9.

Serological discrimination by indirect enzyme immunoassay between the antibody response to Brucella sp. and Yersinia enterocolitica O:9 in cattle and pigs

A rapid, inexpensive and rugged serological test that distinguishes cattle and swine infected with Brucella sp. or Yersinia enterocolitica O:9 is described. The test protocol, which is an indirect enzyme immunoassay uses a high concentration of divalent cation chelating agents to minimize binding of Y. enterocolitica O:9 antibody to rough lipopolysaccharide antigen derived from B. abortus RB51. No false positive reactions were observed when testing 100 Canadian cattle and swine without any evidence of brucellosis. The assay detected 91.6% of cattle (n=155) and 93.5% (n=31) of swine infected with Brucella sp. Sera from 58 cattle and 38 swine exposed to Y. enterocolitica O:9 were negative while only 20 sera from 121 'false positive' reactors of unspecified origin gave low level positive reactions, eliminating 84% of the false positive reactions.

Brucella melitensis infection associated with Guillain-Barré syndrome through molecular mimicry of host structures

Brucella melitensis is a facultative intracellular bacterium that can survive inside macrophages and the causative agent of brucellosis. In the present study, we found that a lipooligosaccharide of B. melitensis has a GM1 ganglioside-like structure and shows a strong antibody response in mice. The cholera toxin B subunit, which binds to GM1 ganglioside specifically, reacted with the surface of B. melitensis. Immunization with B. melitensis induced the production of anti-GM1 ganglioside antibodies in mice and serum from immunized mice showed a cross-reaction with Guillain-Barré syndrome (GBS)-associated Campylobacter jejuni, but not non-GBS-associated C. jejuni. When B. melitensis was treated with a neuraminidase, antibody responses disappeared. B. melitensis immunization induced the production of anti-GM1 ganglioside antibodies in BALB/c mice but not in C57BL/6 and ddY mice, and for BALB/c mice, immunization with B. melitensis induced much greater production of anti-GM1 ganglioside than GBS-associated C. jejuni. Flaccid limb weakness was observed in B. melitensis immunized mice. These results suggest that B. melitensis is a new etiological agent for GBS and that immunological responses between it and GBS-associated C. jejuni in the mouse model may be different.

La brucellose à l’aube du 21e siècle

Human brucellosis is now a rare disease in countries where eradication programs (especially vaccination) against brucellosis in cattle, sheep, and goats have been successfully implemented. In France, fewer than 50 brucellosis cases are annually notified to the National Institute for Infection Surveillance. Human brucellosis, however, remains endemic in the Mediterranean basin, Middle East, Western Asia, Africa, and South America. Shortcomings of standard diagnostic methods for brucellosis (variable sensitivity of culture, frequent serological cross reactions) have been only partially resolved by modern molecular biology techniques. There are now 3 new challenges to be faced by the medical and veterinarian community: the expanding wildlife reservoir of brucellosis, with a possible impact on domestic animals; the emergence of Brucella. melitensis infections in cattle, for which prophylactic efficacy of available vaccines has not been established; and recent recognition of a huge animal reservoir of Brucella species in marine mammals, for which the potential virulence in humans remains unknown.

Epidemiological and serological survey of brucellosis in Mongolia by ELISA using sarcosine extracts

Brucellosis is an important zoonosis, and serological surveillance is essential to its control. However, cross-reactions of attenuated live cells of Brucella abortus strain S-19 and B. melitensis strain Rev-1 with Yersinia enterocolitica O9 or vaccinated animal sera interfere with accurate serological diagnosis by the Rose Bengal test (RBT). Therefore, we used ELISA with sarcosine extracts from the virulent B. abortus strain 544 to eliminate false-positives among RBT positive-sera. A total of 697 serum samples were collected in Mongolia from humans and animals in 23 nomadic herds. The herds were classified into three groups as brucellosis-endemic (BE), brucellosis-suspected (BS), or Brucella-vaccinated (BV). The number of 295 animals (43.0%) was positive by RBT, but 206 (69.8%) of these were positive according to ELISA; therefore, 30.2% of the RBT-positive sera were found to be false positives. The false positive samples for RTB represent 4.1%, 27.4%, and 68.2% of the animals from the BE, BS, and BV herds, respectively. In addition, 32% of RBT-positive human sera were also false positives. Thus, our ELISA would be more specific than RTB and useful for epidemiological surveillance for brucellosis.